APS March Meeting 2018

Monday–Friday, March 5–9, 2018;
Los Angeles, California

Abstract: T60.00312 : Effects of Dimensional Confinement on the Reactivity of Carboxylic-Acid-Functionalized Molecules

Abstract

Presenter:

Dominic Goronzy(Chemistry and Biochemistry, University of California, Los Angeles)

Authors:

Dominic Goronzy(Chemistry and Biochemistry, University of California, Los Angeles)

Erin Avery(Chemistry and Biochemistry, University of California, Los Angeles)

Nathan Gallup(Chemistry and Biochemistry, University of California, Los Angeles)

Jan Staněk(Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic)

Jan Macháček(Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic)

Tomáš Baše(Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic)

Kendall Houk(Chemistry and Biochemistry, University of California, Los Angeles)

Paul Weiss(Chemistry and Biochemistry, University of California, Los Angeles)

Self-assembled monolayers (SAMs) provide a system to explore the effects of dimensionality on chemical functional groups. We probed interactions within carboxylic-acid-functionalized carboranethiol SAMs as well as the interactions between the monolayer and the environment. Monolayers composed entirely of meta-functionalized carboranethiols were imaged via scanning tunneling microscopy (STM). Unlike para-functionalized carboranethiols, which adopted the same nearest-neighbor spacing as unfunctionalized carboranes (7.2 Å), meta-functionalized carboranethiols have a larger spacing of 8.4 Å. Studies with two isomers of meta-carboranethiols yielded similar results. To examine the impact of dimensionality on the carboxylic acid group’s acidity, we employed contact angle titration. We found a pKa shift of nearly four pH units from 3.01-3.23 in solution to approximately 6.95 on the surface. Density functional theory calculations tested the effect of desolvation by two-dimensional (2D) confinement, showing a shift in pKa consistent with experimental results. STM-observed differences in SAMs deposited in ethanol versus benzene provided further evidence for profound changes in carboxylic acid reactivity when placed in the 2D confinement imposed by the thin-film configuration.